Fix duplicate invites (#1437)

Co-authored-by: Josh Pigford <[email protected]>

app/models/invitation.rb

@@ -5,6 +5,7 @@ class Invitation < ApplicationRecord
   validates :email, presence: true, format: { with: URI::MailTo::EMAIL_REGEXP }
   validates :role, presence: true, inclusion: { in: %w[admin member] }
   validates :token, presence: true, uniqueness: true
+  validates_uniqueness_of :email, scope: :family_id, message: "has already been invited to this family"
   validate :inviter_is_admin
 
   before_validation :generate_token, on: :create

db/migrate/20241108150422_add_unique_email_index_to_invitations.rb

@@ -0,0 +1,5 @@
+class AddUniqueEmailIndexToInvitations < ActiveRecord::Migration[7.2]
+  def change
+    add_index :invitations, [ :email, :family_id ], unique: true
+  end
+end